System for regulating the supply of liquid fuel to a gas turbine



J. SYSTEM FOR REGULATING THE SUPPLY Aug 7, 1956 H. JAGGER 0F LIQUID FUELTO A GAS TURBINE 2 Sheets-Sheet 1 Filed Jan. '7, 1952 CONNECTED TOCOMP/P515501? OUTLET 10 4:2

INVENTOR HY :TA 66 E R B), Why/.4, 2 mwlh'fl Aug. V, 1956 .1. H. JAGGER2,757,511

SYSTEM FOR REGULATING THE SUPPLY OF LIQUID FUEL. TO A GAS TURBINE FiledJan. '7, 1952 2 Sheets-Sheet 2 C'fi/V/VECTED T0 COMPRESSOR OUTLET com/5cTED T0 comp/95550;? lNTA/(E IN E NTo R I HUI/#6651? States Patent SYSTEMFOR REGULA'HNG THE SUPPLY OF LIQUID FUEL TO A GAS TURBINE James H.Jagger, Coventry, England, assiguor to Armstrong Sitideley MotorsLimited, Coventry, England Application January '7, 1952, Serial No.265,330

Claims priority, application Great Britain lanuary 26, 1951 1 Claim.(Cl. 6il--39.28)

This invention relates to a system, for regulating the supply of liquidfuel to a gas turbine engine, of the kind including a constant-delivery,engine-driven pumping unit the effective delivery or which is controlledby a pressure-responsive control plunger, without any spring control,which serves as a spill valve and which has the effective deliverypressure applied to one face, whilst the opposite end of the chamber inwhich the control plunger works is connected to the end at which theeliective delivery pressure is supplied through a restrictor orifice,and it also communicates with a passage (hereinafter referred to as thecontrol passage) the pressure in which can be regulated dependently uponoperating conditions. To increase the etlective delivery the pressure inthe control passage must be increased.

Such a pumping unit is provided with means to control the fuel flow at apredetermined maximum engine speed in order to prevent overspceding ofthe engine, the means acting upon the pressure in the control passage,or in another control passage provided in parallel therewith.

The main object of the invention is to prevent the engine from stalling,due to overfuelling, when the throttle control is rapidly opened.

The invention comprises the combination with a regulating system of thekind specified in the first paragraph of this specification, of anair/fuel ratio device through which the effective delivery of thepumping unit is passed, the device having a variable choke adapted toset up a pressure dilierence between the inlet and outlet sides of thechoke without the choke being affected by the said pressure difference,and the pressure difference is applied for actuating a valve for thecontrol passage, or for another control passage in parallel therewith,the choke being actuated responsively to a function of the outputpressure of the compressor of the engine,

In the drawings:

Figure l shows, diagrammatically, one form of apparatus for carrying theinvention into practice;

Figure 2 is a graph illustrating the corresponding operating conditions;

Figure 3 shows, diagrammatically, a modified apparatus;

Figure 4 is a graph illustrating the operating conditions of theapparatus in Figure 3; and

Figure 5 is a section on the line 5-5 of Figure 1.

in Figure l is shown a constant delivery, enginedriven pumping unit,indicated generally at A, and an air/fuel ratio device at The pump has arotor ll. which is concentrically fast with a driven shaft 112, the twobeing formed separately but having a toothed engagement at 13 to lockthem together. The bore of the rotor, also concentric with the shaft, isjournalled on a core M.- which is fast at one end with the pump bodylit. The rotor has radial bores M in which work pistons if? having, attheir heads, slippers 18 which are journalled on transverse pins 19 ofthe pistons and make frictional contact with a bore 20 of the pump body,this bore being eccentric with respect 'ice to the shaft. Thus, as theshaft 12 is rotated, the slippers, in riding round the bore 2d, causethe pistons 17 to be reciprocated in the radial bores 16 of the rotor.

Fuel is fed from a line 21 to a duct 22 in the core, from which duct itis delivered through ports 23 to the radial bores 16 when the pistonsare at their radially outmost position, and rotation of the rotor causesthe fuel in the bore 16, on the return stroke of the pistons, to bedelivered, through other ports 24a to a duct 24 in the core, to apressure line 25.

Within the pump body there is a duct 26 which communicates with thedelivery duct 24 and contains a pistontype valve 27 which is biassedagainst the delivery pressure by a spring 28. When the pump deliveryreaches a predetermined pressure, the valve 27' opens to deliver fuel,through a lateral port, to react on an axial end wall 29 of a peripheralgroove in the movable member 30 of a spill or by-pass valve. Thedelivery duct 24 also communicates, through a duct 3i having aconstriction 32, with a duct 33 leading to an opposite end face 34 ofthe spill valve member 30, whereby, when the pressure in the deliveryduct 24 exceeds a predeterm ned value, the pressure drop across theconstriction causes the spill valve member 36 to control the opening ofthe lateral port communicating with the inlet duct 22. Thus the memberIii) can have a hollow end with V-shaped castellations 35 the spacesbetween which, when the member 39 is appropriately moved, establish thecommunication between the ducts 24 and 22.

The pump delivers through the line 25 to a chamber lid of the air/fuelratio device it. This chamber communicates with a line 37, from whichthe combustion chamber burners of the engine are supplied, through aconstriction 38 which is normally open but only to an extent controlledby a valve member 39 which is movable responsively to a function of thepressure of the compressor output. The valve member 39 is generallycylindrical, being a sliding fit in the constriction 38, and it isslotted on opposite sides to form curved portions 390, the axialposition of which in the constriction controls the effective area of thepassage through the latter, the constriction I-lS and member 39 thusconstituting a variable choice.

The slotting of the valve member 39 bifurcates it at the top, Where apin ill, which unites the arms formed by the bifurcation, serves as ananchorage for one end of a spring 41 of which the other end is fast witha lever 52 presently to be described. The valve member 39 is fast with apiston 43 working in a cylinder 44 formed in the body of the air/fuelratio device, and the piston has a small leak path indicated at 46.Movement of the piston 43 causes the valve member 39 to move in theconstriction 38 and thus varies the effective area of the constrictionand, therefore, the pressure drop from the chamber as to the line 37(although this pressure drop is subsequently restored as hereinafterdescribed). The fuel which passes through the leak path as fills thecylinder M, and the latter has outlet path 4'7 which communicates,through a controlled valve orifice 48 (presently to be described) withthe line 37.

The pressure drop across the constriction 3?. is apilied by ducts 4 ,9,Ell to opposite sides of a piston 51 working in a ring-like cylinder 52.The piston 53 is fast with a resilient diaphragm 53, which is trappedbetween the adjacent. end of the cylinder 52 and an interruptedperipheral flange 5d of a cup-like member 555 fast with the body 45, andthe piston 51 is loaded by a spring 56 to balance the pressuredifference when the latter is of a predetermined value.

it the engine throttle (not shown) be opened suddenly for acceleratingthe engine, there is a danger that the engine will be overfuelled andstall. To prevent this,

it is arranged for the fuel supply to the engine, consequent on a suddenopening of the throttle, to be under the control of a function of thecompressor output pressure.

This is done, as shown diagrammatically in Figure l, by communicatingthe compressor output pressure through a duct 57 into a chamber 58 inwhich there is a pressurescnsitive capsule 59. Thus, when the compressoroutput commences to increase consequent on the throttle openingmovement, the capsule is compressed, causing the lever 42 to move aboutits pivot 60 in the body 45 to increase the clearance between ahalf-ball-valve member 61 and the valve orifice 48. This relieves thepressure in the chamber 44 and enables the piston 43 to be depressed,responsively to the pressure in the chamber 36, against the effort ofthe spring 41. This depression of the piston 43 moves the valve member39 to increase the effective area of the constriction 38 in step withthe increasing compressor output pressure.

The depression of the piston 43 increases the tension in the spring 41and thus applies a force to the lever 42 to restore the previousclearance between the halfballvalve member 61 and the orifice 48, butwith the valve member 39 in a new position in which the effective areaof the constriction 38 is increased.

At the same time, this further opening of the constriction reduces thepressure drop across it, and the new pressure drop is applied throughthe ducts 49 and 50 to cause the piston 51 to move, through a push rod62,

an arm 63, pivoted at 64 to the cup-like member 55, moving ahalf-ball-valve member 65 towards the closed position.

The arm 63 is also acted upon by a spring 66 which, through a screwmeans 67, enables the effort of the spring 56 to be adjusted.

When the arm moves the half-ball-valve 65 towards the closed position itconstricts a valve orifice 68 partially to cut off a leak path, througha control passage 100, from beneath the movable member 30 of the spillvalve to pump supply line 21. This causes the pressure beneath the spillvalve member 30 to increase, thus moving it in the direction to reducethe leak path from the duct 26 to the pump intake. In this way a greaterproportion of the pump delivery is supplied through the line 25 to thefuel burners and restores the predetermined pressure difference acrossthe constriction 38, permitting the piston 51 to recover and thehalf-ball-valve 65 to assume a position, relative to the orifice 68, formaintaining the fuel flow from the pump which rc-established thepressure difference across the constriction 38.

During acceleration of the engine, the increasing compressor outputtends to operate the valve 48, 61 in the opening direction, whereby toallow the piston 43 to move for opening more widely the constriction 38.The resultant temporary drop in the pressure difference across theconstriction 38, however, is applied by the piston 51 for decreasing thepassage of the fuel through the orifice 68 back to the line 21 from theline 100 whereby the pump is caused to deliver a greater proportion ofits output to the line 25 to restore the pressure drop across theconstriction 38. In these conditions the supply of fuel to the line 37is increased to maintain an air/fuel ratio which is at all times belowthe stalling characteristic of the engine.

The lever 42 besides being biassed downwardly by the spring 41 is alsobiassed upwardly by a spring '70 with van adjustable anchorage 71,whereby the effort of the spring 41 can be adjusted.

These conditions of operation are illustrated by Figure 2 in which fuelsupply in gallons per hour is plotted I against the compressor outputpressure which, of course,

at any given altitude is related to the engine speed. The

.curves C and D represent, respectively, the engine running and stalllines at sea level, and it will be seen that,

,with the engine running smoothly in the lower speed w 4 range, a suddenopening of the throttle could result in a sufficient supply of fuel tostall the engine before the latter could accelerate sufficiently foradequately increasing the compressor output for burning the extra fuel.The control exerted by the invention is represented by curve B fromwhich it will be seen that the increased supply of fuel, consequent on asudden opening of the fuel valve, is restricted to a value beneath thatat which there is a danger of stalling the engine.

From medium engine speeds upwards, the stall curve rises steeply and, sothat high accelerations from such speeds can be obtained, it is arrangedthat the valve member 39 shall, in that speed range, be in a position inwhich the constriction 38 offers a minimum of resistance to the fuelflow to the line 37, and this is represented by the steeper portion ofthe curve E.

To prevent more fuel being supplied to the burners than the engine needsat a predetermined maximum speed, there is a disc 72 which is maderotatively fast with the pump shaft 12, by angularly-spaced balls 73engaging longitudinal grooves of the shaft and of the disc. The spacebetween the balls 73 communicates, through a duct 74, with the supplyline 21 to the pump, the communication being through a diaphragm chamber75, a clearance space 76, a chamber 77 and a duct 78. The disc 72 hasradial bores 79 in which a centrifugal pressure is developed andtransmitted, through an annular gallery 80 in the body 15, and a duct 81to an opposed diaphragm chamber 82.

The diaphragm 83 separating the chambers 77 and 82 is biassed by atension spring 84, having an adjustable anchorage 85. A compressionspring 86 biasses a lever 87 about its pivot 88 to close a valve 89 in aduct 90 leading from the duct 31 with the constriction 32. When there isany tendency to over-speed and the pressure difierence in the chambers'77 and 82 exceeds a predetermined figure, as controlled by the spring84, a stem 91 contacting the diaphragm 83 rocks the lever 87 to unseatthe valve 89, allowing some of the fluid in line 33 to return to theintake line through the chamber 77 and duct 78. This reduces thepressure under the spill valve 30, enabling it to by-pass a greaterproportion of the pump output to the intake line. In thesecircumstances, therefore, the fuel flow is controlled by the pump speedonly, overriding the air/ fuel ratio control.

The previously described acceleration control, operating with thecompressor output pressure only, does not operate satisfactorily at highaltitudes owing to the air/fuel ratio control limiting the maximum speedof the engine. This is illustrated by Figure 4 in which the curves D1,Cl are the ones which correspond with curves D and C at a particularhigh altitude. It will be seen that the curve C1 is intercepted by thecurve E so that the engine speed cannot rise above the valuecorresponding with the point of interception. With increasing altitude,therefore, it is necessary to modify the curve B by bringing its steeplyrising portion nearer the origin so as to lie between the curves D1 andC1 as shown. This can be done by the pressure sensitive arrangementshown in Figure 3, which enables the air/fuel ratio control to actresponsively to the compression ratio of the compressor.

The pressure sensitive arrangement of Figure 3 includes a pressuresensitive capsule 128 which has a common wall 121 with a second, andsmaller capsule 122 which is evacuated. The wall 121 carries a movablevalve member 123 which, at a predetermined compression ratio closes theoutlet of a venturi passage 124 which otherwise establishes acommunication between the interior of the capsule and the compressoroutlet through a duct 125. The throat of the venturi passagecommunicates with an annulus 126 which, in turn, communicates through aduct 128 with the chamber 58. Thus when the valve member 123 is in openposition the .static pressure in the venturi throat is transmitted tothe chamber 58, and when the valve 123 is in closed position thecompressor output pressure is transmitted to the said chamber 58.

Pressure from the duct 125 is also delivered, through an adjustableneedle valve 127, to the exteriors of the capsules 120 and 122, thepressure in the chamber around the capsules acting on the capsuleassembly in the direction for closing the valve member 123. The airwhich has passed the needle valve 127 also passes into the interior ofthe capsule 120 through a restrictor orifice 129, the interior of thesaid capsule 120 communicating, through a duct 130, with the compressorintake.

During a rapid acceleration of the engine the pressure ratio of thecompressor increases with speed, and while the valve 123 is in openposition a lower pressure than the compressor output pressure istransmitted to the chamber 58 from the throat of the venturi 124. Thislower pressure is arranged to produce a fuel flow to the engine at alltimes below the stall line of the engine. At the same time, a reducedvalue of the compressor output pressure is also acting on the exteriorof the capsule assembly 120, 122 and at a value of the compressorpressure ratio at which a sudden increase in fuel flow will not producestall conditions, this pressure closes the valve 123. As the valve 123closes, the pressure in the chamber 58 rises to the actual value of thecompressor outlet pressure since the air flow through the venturiceases, giving a larger opening of the constriction 38 and hence asuddenly increased fuel flow to the engine.

Since the valve 123 is closed responsively to the compressor pressureratio, which in turn is related to the speed of the engine, therelationship of the sudden increase in fuel flow to the engine stallline at any altitude will not vary.

For matching the air/fuel ratio device to any particular engine, theneedle valve 127 can be adjusted in order to secure that the valve 123will close at an appropriate pressure ratio of the compressor.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is:

A regulating system, for the supply of liquid fuel to a gas turbineengine including an air compressor and a burner for the fuel, comprisingthe combination of a constant-delivery pumping unit, to be driven fromthe engine, and an air/ fuel ratio device for regulating the fuel supplydependently on the air available at the compressor outlet at both steadyand fluctuating speeds, said unit including a delivery passage and aspill passage, a pressureresponsive control plunger for controlling saidspill passage and thus the elfective delivery through said deliverypassage, a communication from said delivery passage to one face of saidplunger, a communication, containing a restrictor orifice, from saiddelivery passage to an opposite face of said plunger, a valve in saidair/fuel ratio device, a control passage communicating between saidopposite face of said plunger and said valve of said air/fuel ratiodevice, a variable choke in said device, said choke in the path of acommunication between said delivery passage and said burner, said chokeadapted to set up a pressure difference between its inlet and outletsides without said choke being affected by said pressure difference,means responsive to such pressure difference for actuating said valve ofsaid device, a piston fast with a movable member of said choke, saidpiston having a leak path in parallel with said choke, a movable valvemember controlling said leak path, a pressure sensitive device, saidsensitive device being a pneumatic capsule which is biassed to anextended position, said capsule being in a chamber to which is ledthrough a change-over device a pressure which is a function of thecompressor output pressure, said change-over device including a pair ofaligned, opposed pneumatic capsules of different sizes, a common wall atthe adjacent ends of said pair of capsules, a coaxial duct in the largercapsule of said pair, a valve member fast with said common wall andcoacting with the adjacent end of said duct, the remote end of saidcapsule to receive air at the compressor output pressure, said duct ofventuri formation and having a lateral communication with said chamber,an envelope containing said pair of capsules, a restrictor through whichthe compressor output air passes with pressure reduction to be appliedto the exterior of said pair of capsules, and a restrictor through whichair from said envelope passes with further pressure reduction to theinterior of the larger of said pair of capsules, the interior of thelarger of said pair of capsules communicating with the compressorintake, whereby, above a predetermined pressure ratio of saidcompressor, the valve member fast with said common Wall closes saidadjacent end of said duct to cause the compressor output pressure to beapplied to said chamber, and below said predetermined pressure ratiosaid valve member fast with said common wall opens said adjacent end ofsaid duct to cause a lower pressure than that of said compressor outputto be applied to said chamber, and a lever interconnecting said pressuresensitive device and said movable member whereby to vary the effectivesize of said leak path for enabling said movable member to adjust itselffor maintaining constant the pressure difference between the inlet and.outlet sides of said choke.

References Cited in the file of this patent UNITED STATES PATENTS2,429,005 Watson et al Oct. 14, 1947 2,450,535 Watson et al. Oct. 5,1948 2,503,048 Ifield Apr. 4, 1950 2,604,756 Greenland July 29, 1952

